Perhaps worth mentioning too that some addon RapidWeaver themes include the free FitVids.js plugin as standard, therefore removing the need to re-generate embed codes. In such instances, you would be able to continue using standard YouTube / Vimeo code and the theme will make them responsive for you.
Yes all my themes have included FitVids and some other responsive / retina optimisations for a couple of years. I believe there are some other theme developers who provide the same in their designs too.
OK, tried this and it worked fine, except for one small fiddle: the left edge of the video is being cut off. I’ve played with the ‘left’ position setting and the video sizing parameters to no avail. I think that the theme may be responsible and I’ve solved the same problem elsewhere with increasing the left padding, but can’t seem to get that working here.
Presumably this is a helper class in the theme. It normally applies a negative horizontal margin of 40px to pull content to the extreme edges of a container. It might not be compatible with blogs or within the context in which you are using it. So it either needs to be overridden with CSS code or if you can modify your HTML embed code for the video, remove the following…